With the development of 3G technology, in order to meet the ever-increasing requirement of multimedia services on high-speed data transmission, 3rd Generation Partnership Project (3GPP) discloses a High Speed Downlink Packet Access (HSDPA) technology. The main object of HSDPA is to provide a guarantee of higher data transmission rate, lower time delay, higher system throughput and more powerful Quality of Service (QoS).
In the HSPDA, a High Speed-Downlink Shared Channel (HS-DSCH) is used for data transmission. The HS-DSCH is a transmission channel, and may be mapped to one or more physical channels and shared by a plurality of User Equipments (UEs) in Time Division Multiplexing mode and in Code Division Multiplexing mode. To realize rapid control on the HS-DSCH, a High Speed-Shared Control Channel (HS-SCCH) is set as a dedicated downlink control channel for the HS-DSCH to bear control information of the HS-DSCH, and a High Speed-Shared Information Channel (HS-SICH) is set as a dedicated uplink control channel for the HS-DSCH to feed back quality information of the downlink channels and a response for data blocks of downlink transmission to a NodeB. Furthermore, a Dedicated Physical Channel (DPCH) exists in the uplink channel and the downlink channel respectively, the DPCH is used for transmitting control information such as Radio Resource Control (RRC) signaling, and may also support the service transmission such as voice service and data service.
The power control function in the HSDPA is mainly embodied in the initial transmit power allocation, open loop power control and closed loop power control of the control channels such as HS-SCCH, HS-SICH, uplink DPCH and downlink DPCH. The open loop power control refers to that a UE adjusts its own transmit power by measuring the path loss variance. The closed loop power control refers to that a UE or a NodeB adjusts its own transmit power according to a Transmit Power Control (TPC) command sent by the opposite end. The initial transmit power of HS-SCCH is set by a NodeB according to the transmission capacity of the NodeB and the number of code channels occupied by the HS-SCCH, and the initial transmit power of downlink DPCH is set by a NodeB according to the transmission capacity of the NodeB and the number of code channels occupied by the downlink DPCH. The initial transmit power of HS-SICH or uplink DPCH is set according to the open loop power control.
In the prior art, a method for power control on a control channel is shown in FIG. 1, the method specifically includes a UE transmitting information on an uplink control channel according to a certain transmit power, the information being received by a NodeB after the information passes through a radio control channel. The NodeB estimates the Signal to Interference Ratio (SIR) according to the received information, compares the estimated SIR with a target value of SIR configured by a Radio Network Controller (RNC) to generate a TPC command, and the TPC command is transmitted to the UE via a downlink control channel. The UE obtains a power deviation PTPC that the UE needs to adjust according to the TPC command and a power control step-length configured by an RNC, compensates the current transmit power of the uplink control channel according to the PTPC to obtain a new transmit power. On the NodeB side, the target value of SIR may be adjusted to meet the performance requirements of the downlink control channel according to the statistical information of coding result of the uplink control channel.
The power control on the uplink control channel is carried out in the following modes.
When a UE transmits information on an uplink control channel for the first time after the UE receives information on a downlink control channel for the first time, because the received information carried in the downlink control channel is an invalid TPC command, the closed loop power control on the uplink control channel cannot be accomplished according to the invalid TPC command, the UE performs the power control on the uplink control channel transmission via the open loop power control.
After the UE receives a TPC command on the downlink control channel, the UE adjusts the transmit power of the uplink control channel correspondingly according to the TPC command and the power control step-length set by an RNC.
When the UE needs to carry out uplink control channel transmission again after the UE is subjected to one or more receiving pauses of the downlink control channels, because the effective power control on the uplink control channel cannot be implemented according to the previous TPC command, the UE controls the current uplink control channel transmission by using the open loop power control.
The main reasons that may cause a transmitting pause of the downlink control channels include: 1) multi-UE sharing may cause multi-UE time-division scheduling interval, although the HS-SCCH Cyclic Sequence Numbers (HCSNs) of the downlink control channels may be continuous, the discontinuous scheduling on the UE may cause deviation of the control on the downlink control channel, which may cause discontinuous transmission of the downlink control channel; 2) the receiving error of the downlink control channel may cause discontinuous HCSN, so that an interval may appear on the power control of uplink control channel transmission after the UE receives information on a downlink control channel correctly.
The power control on the downlink control channel is carried out in the following modes.
When a NodeB performs downlink control channel transmission for the first time, the NodeB sets the initial transmit power of the downlink control channel according to the transmission capacity of the NodeB and the number of code channels occupied by the downlink control channel, and the initial transmit power should not exceed the maximum transmit power of the downlink control channel configured by an RNC. After the downlink control channel transmission is carried out for the first time, the NodeB may control the downlink control channel by using the closed loop power control, that is, the NodeB may adjust the subsequent transmit power of the downlink control channel according to a TPC command carried in the uplink control channel that is sent by a UE. The main purpose of the setting of TPC command is to make the receiving of the downlink control channel reach a target value of Block Error Rate (BLER).
In summary, since the time-division scheduling is used for UE in the HSDPA, discontinuous transmission exists in HS-SICH, HS-SCCH, uplink DPCH and downlink DPCH for the same UE. In the prior art, the power control is performed on an uplink control channel by using open loop power control so long as discontinuous receiving appears on a downlink control channel. Correspondingly, a NodeB performs the downlink control channel transmission by using the initial transmit power so long as discontinuous downlink control channel transmission appears. Such a method cannot well utilize the control gain obtained by carrying out the power adjustment using the TPC command in the closed loop power control in a certain related time. Therefore, in the prior art, when the control channel transmission is discontinuous, the power control on the control channel cannot be effectively performed.